Fraction Of Effective Force Research Articles

Shoulder pain in persons with tetraplegia and the association with force application during manual wheelchair propulsion

Introduction
 Shoulder pain is highly prevalent in persons with spinal cord injury (Liampas et al., 2021) and restricts daily mobility and thus participation and quality of life. Shoulder loading activities, such as manual wheelchair propulsion or transfers, are seen as risk factors for shoulder pain. To minimize the risk for shoulder pain, clinical guidelines instruct persons with spinal cord injury to “use long, smooth strokes that limit high impacts on the pushrim”. Findings supporting this recommendation have been found for persons with paraplegia (Beirens et al., 2021). However, dependent on their lesion level, persons with tetraplegia do not have, full triceps function and are not able to grasp the hand rim properly, which will alter force application and may further impact shoulder pain. The aim of this study was to investigate the association between wheelchair propulsion biomechanics, including force application and spatio-temporal characteristics, and shoulder pain in persons with tetraplegia.
 Methods
 Sixteen community-dwelling, wheelchair dependent participants with tetraplegia (C7-C5, age 49.1 ±2.9 years, 23.4 ±2.4 years since injury, 94% male) were measured during wheelchair propulsion on a treadmill at two speed / power output conditions: 0.56 ms-1/10W and 0.83 ms-1/15W. A Smartwheel was fitted to the personal wheelchair to measure force application. The applied forces, their effectiveness (fraction of effective force) and smoothness (rate of rise of force, jerk), as well as push frequency, push angle and timing of the push cycles were analyzed. Based on the Wheelchair User Shoulder Pain Index (0-150), participants were stratified in groups with low (≤ 7), moderate (8-35) and high (≥ 36) shoulder pain. A mixed-effect multilevel analysis was used to identify the association between the dependent variables (propulsion biomechanics) and group of shoulder pain when controlling for sex, age, time since injury, lesion level, body weight and height.
 Results and Discussion
 The analysis showed that persons with high shoulder pain applied the force over a longer push angle (85.6°) and had a shorter recovery time (0.4s) and applied the force more effective (FEF = 40.7%) than persons with low pain (push angle = 81.2°, recovery time = 0.5s, FEF = 35.2%). In addition, persons with high shoulder pain applied less medial directed force (6.4 N) compared to persons with moderate pain (14.9 N). The results of this cross-sectional study on wheelchair propulsion in persons with tetraplegia are in contradiction to previously reported results in person with paraplegia (Beirens et al., 2021). Interestingly, tetraplegic persons with high shoulder pain are following clinical recommendation on how to propel the wheelchair optimally. These results support the importance of differentiating between lesions levels when further investigating force application as a risk factor for shoulder pain. In addition, the results ask for a close examination and possible adaptation of the clinical guidelines for persons with tetraplegia.
 References
 Beirens, B. J. H., Bossuyt, F. M., Arnet, U., van der Woude, L. H. V., & de Vries, W. H. K. (2021). Shoulder pain is associated with rate of rise and jerk of the applied forces during wheelchair propulsion in individuals with paraplegic spinal cord injury. Archives of Physical Medicine and Rehabilitation, 102(5), 856-864. https://doi.org/10.1016/j.apmr.2020.10.114
 Liampas, A., Neophytou, P., Sokratous, M., Varrassi, G., Ioannou, C., Hadjigeorgiou, G. M., & Zis, P. (2021). Musculoskeletal pain due to wheelchair use: A systematic review and meta-analysis. Pain and Therapy, 10, 973-984. https://doi.org/10.1007/s40122-021-00294-5

Impact of Holding a Badminton Racket on Spatio-Temporal and Kinetic Parameters During Manual Wheelchair Propulsion.

IntroductionPara badminton entered the Paralympic world for the first time with the 2021 Paralympic Games in Tokyo. The particularity of this sport lies in the handling of the wheelchair and the racket simultaneously. To the best of our knowledge, and considering the youthfulness of this sport, it appears that no study has looked at the impact of the badminton racket on the kinetic and spatiotemporal parameters. Therefore, the aim of our study was to investigate the impact of the badminton racket on the amplitude of kinetic and spatiotemporal parameters of wheelchair propulsion, considered as propulsion effectiveness and risk of injury criteria. We hypothesized that holding a badminton racket while propelling the wheelchair modifies the kinetics and temporal parameters of the athlete's propulsion due to the difficulty to hold the handrim, therefore decreasing propulsion effectiveness and increasing risk of injury.Materials and MethodsFor six 90-min sessions, 16 able-bodied individuals were introduced to badminton. No injuries hindered their propulsion. They had to propel with and without a racket held on the dominant side along a 20 m straight line at a constant velocity of 5 km/h. They all used the same sports wheelchair equipped with two instrumented wheels (SmartWheel).ResultsParticipants increased their maximal total force and force rate of rise but decreased their fraction of effective force with their dominant hand compared to the non-dominant hand when using a racket. In addition, they decreased their fraction of effective force, push time, cycle time, and push angle, and increased their maximal propulsive moment, maximal total force, and force rate of rise when comparing the same dominant hand with and without the racket.DiscussionUsing a badminton racket modifies the athlete's force application in a way that is generally related to lower propulsion effectiveness and a higher risk for injury. Indeed, it seems that propulsion with a racket prevents from correctly grabbing the handrim.

Physiological and biomechanical comparison of overground, treadmill, and ergometer handrim wheelchair propulsion in able-bodied subjects under standardized conditions

BackgroundHandrim wheelchair propulsion is often assessed in the laboratory on treadmills (TM) or ergometers (WE), under the assumption that they relate to regular overground (OG) propulsion. However, little is known about the agreement of data obtained from TM, WE, and OG propulsion under standardized conditions. The current study aimed to standardize velocity and power output among these three modalities to consequently compare obtained physiological and biomechanical outcome parameters.MethodsSeventeen able-bodied participants performed two submaximal practice sessions before taking part in a measurement session consisting of 3 × 4 min of submaximal wheelchair propulsion in each of the different modalities. Power output and speed for TM and WE propulsion were matched with OG propulsion, making them (mechanically) as equal as possible. Physiological data and propulsion kinetics were recorded with a spirometer and a 3D measurement wheel, respectively.ResultsAgreement among conditions was moderate to good for most outcome variables. However, heart rate was significantly higher in OG propulsion than in the TM condition. Push time and contact angle were smaller and fraction of effective force was higher on the WE when compared to OG/TM propulsion. Participants used a larger cycle time and more negative work per cycle in the OG condition. A continuous analysis using statistical parametric mapping showed a lower torque profile in the start of the push phase for TM propulsion versus OG/WE propulsion. Total force was higher during the start of the push phase for the OG conditions when compared to TM/WE propulsion.ConclusionsPhysiological and biomechanical outcomes in general are similar, but possible differences between modalities exist, even after controlling for power output using conventional techniques. Further efforts towards increasing the ecological validity of lab-based equipment is advised and the possible impact of these differences -if at all- in (clinical) practice should be evaluated.

Effects of an Upper-Body Training Program Involving Resistance Exercise and High-Intensity Arm Cranking on Peak Handcycling Performance and Wheelchair Propulsion Efficiency in Able-Bodied Men.

Chaikhot, D, Reed, K, Petroongrad, W, Athanasiou, F, van Kooten, D, and Hettinga, FJ. Effects of an upper-body training program involving resistance exercise and high-intensity arm cranking on peak handcycling performance and wheelchair propulsion efficiency in able-bodied men. J Strength Cond Res 34(8): 2267-2275, 2020-The aim of this study was to determine the training effects of an upper-body training program involving resistance exercise and high-intensity arm cranking on peak handcycling performance, propulsion efficiency, and biomechanical characteristics of wheelchair propulsion in able-bodied men. The training group (n = 10) received a 4-week upper-body resistance training (RT), 70% of 1 repetition maximum, 3 sets of 10 repetitions, 8 exercise stations, 2 times per week, combined with high-intensity interval training (HIIT) 2 times per week. High-intensity interval training consisted of arm-crank exercise, 7 intervals of 2 minutes at 80-90% of peak heart rate (HRpeak) with 2-minute active rest at 50-60% of HRpeak. The control group (n = 10) received no training. Both groups performed a preincremental and postincremental handcycling test until volitional exhaustion to evaluate fitness and a 4-minute submaximal wheelchair propulsion test at comfortable speed (CS), 125 and 145% of CS, to evaluate gross mechanical efficiency (GE), fraction of effective force (FEF), percentage of peak oxygen consumption (% V[Combining Dot Above]O2peak), and propulsion characteristics. Repeated-measures analysis of variance was performed (p < 0.05). Training resulted in a 28.2 ± 16.5% increase in peak power output, 13.3 ± 7.5% increase in V[Combining Dot Above]O2peak, 5.6 ± 0.9% increase in HRpeak, and 3.8 ± 1.5% decrease in HRrest. No training effects on FEF, GE, % V[Combining Dot Above]O2peak, and push characteristics were identified. In conclusion, the combined RT and arm-cranking HIIT improved fitness. However, it seems that this training did not result in improvements in propulsion efficiency and push characteristics. Additional wheelchair skill training may be needed to fully benefit from this advantage in daily life propulsion.

Start-up propulsion biomechanics changes with fatiguing activity in persons with spinal cord injury

Objective: Shoulder pathology is a common condition in wheelchair users that can considerably impact quality of life. Shoulder muscles are prone to fatigue, but it is unclear how fatigue affects start-up propulsion biomechanics. This study determines acute changes in start-up wheelchair propulsion biomechanics at the end of a fatiguing propulsion protocol. Design: Quasi-experimental one-group pretest-postest design. Setting: Biomechanics laboratory. Participants: Twenty-six wheelchair users with spinal cord injury (age: 35.5 ± 9.8 years, sex: 73% males and 73% with a paraplegia). Interventions: Protocol of 15 min including maximum voluntary propulsion, right- and left turns, full stops, start-up propulsion, and rests. Outcome measures: Maximum resultant force, maximum rate of rise of applied force, mean velocity, mean fraction of effective force, and mean contact time at the beginning and end of the protocol during start-up propulsion. Results: There was a significant reduction in maximum resultant force (P < 0.001) and mean velocity (P < 0.001) at the end of the protocol. Also, contact time was reduced in the first stroke of start-up propulsion (P < 0.001). Finally, propelling with a shorter contact time was associated with a greater reduction in performance (maximum velocity) at the end of the protocol. Conclusion: There are clear changes in overground propulsion biomechanics at the end of a fatiguing propulsion protocol. While reduced forces could protect the shoulder, these reduced forces come with shorter contact times and lower velocity. Investigating changes in start-up propulsion biomechanics with fatigue could provide insight into injury risk.

A physiological and biomechanical comparison of over-ground and treadmill during asynchronous wheelchair propulsion

Two main modes of propulsion in manual wheelchair (MWC) are described in the literature: synchronous mode (Syn) in which arms are working together, and asynchronous mode (Asy) in which arms are working alternating. It has not yet been demonstrated that the propulsion technique used was identical on a treadmill and in the field, especially because of the movement of “steering” on the field during Asy propulsion. The aim of this study is to compare biomechanical and physiological responses of Asy during tests on the field vs. treadmill. Ten wheelchair basketball players performed 1 session of 4 minutes at 8 km.h −1 on the treadmill and 1 session on the field (‘figure 8’ tests). The MWC is equipped with an instrumented wheel allowing measuring temporal parameters: push time (PT), recovery time (RT) and cycle time (CT = PT + RT). Push frequency (PF), Rate of Rise (RoR), Fraction of Effective Force (FEF) and Rolling Resistance (RR) are also measured. Each subject is equipped with a K4, allowing to obtain the consumption of oxygen (VO 2 kg −1 ). The parameters collected are presented in Table 1 . Although the RR is higher for treadmill, Vo2.kg −1 and PT are superior on the over-ground. This can be explained by the steering on the field, which induces an increased use of the trunk muscles for stability. This could also explain lower PF and RoR. Therefore, field test is recommended to evaluate Asy propulsion.

Sex differences in wheelchair propulsion biomechanics and mechanical efficiency in novice young able-bodied adults

An awareness of sex differences in gait can be beneficial for detecting the early stages of gait abnormalities that may lead to pathology. The same may be true for wheelchair propulsion. The aim of this study was to determine the effect of sex on wheelchair biomechanics and mechanical efficiency in novice young able-bodied wheelchair propulsion. Thirty men and 30 women received 12 min of familiarisation training. Subsequently, they performed two 10-m propulsion tests to evaluate comfortable speed (CS). Additionally, they performed a 4-min submaximal propulsion test on a treadmill at CS, 125% and 145% of CS. Propulsion kinetics (via Smartwheel) and oxygen uptake were continuously measured in all tests and were used to determine gross mechanical efficiency (GE), net efficiency (NE) and fraction of effective force (FEF). Ratings of perceived exertion (RPE) were assessed directly after each trial. Results indicated that CS for men was faster (0.98 ± 0.24 m/s) compared to women (0.71 ± 0.18 m/s). A lower GE was found in women compared to men. Push percentage, push angle and local RPE were different across the three speeds and between men and women. NE and FEF were not different between groups. Thus, even though their CS was lower, women demonstrated a higher locally perceived exertion than men. The results suggest sex differences in propulsion characteristics and GE. These insights may aid in optimising wheelchair propulsion through proper training and advice to prevent injuries and improve performance. This is relevant in stimulating an active lifestyle for those with a disability.

Different cadences and resistances in sub-maximal synchronous handcycling in able-bodied men: Effects on efficiency and force application.

BackgroundWith the introduction of an add-on handcycle, a crank system that can be placed in front of a wheelchair, handcycling was made widely available for daily life. With it, people go into town more easily, e.g. to do groceries; meet up with friends, etc. They have more independency and can be socially active. Our aim is to explore some settings of the handcycle, so that it can be optimally used as a transportation device. Therefore, the effects of cadence and added resistance on gross mechanical efficiency and force application during sub-maximal synchronous handcycling were investigated. We hypothesized that a cadence of 52 rpm with a higher resistance (35 W) would lead to a higher gross mechanical efficiency and a more tangential force application than a higher cadence of 70 rpm and no extra resistance (15 W).MethodsTwelve able-bodied men rode in an instrumented add-on handcycle on a motorized level treadmill at 1.94 m/s. They performed three sessions of three four-minute blocks of steady state exercise. Gear (70, 60 and 52 rpm) was changed in-between the blocks and resistance (rolling resistance +0 W, +10 W, +20 W) was changed across sessions, both in a counterbalanced order. 3D force production, oxygen uptake and heart rate were measured continuously. Gross mechanical efficiency (ME) and fraction of effective force (FEF) were calculated as main outcomes. The effects of cadence and resistance were analyzed using a repeated measures ANOVA (P<0.05) with Bonferroni-corrected post-hoc pairwise comparisons.ResultsWith a decrease in cadence a slight increase in ME (70 rpm: 5.5 (0.2)%, 60 rpm: 5.7 (0.2)%, 52 rpm: 5.8 (0.2)%, P = 0.008, η2p = 0.38), while an increase in FEF (70 rpm: 58.0 (3.2)%, 60 rpm: 66.0 (2.8)%, 52 rpm: 71.3 (2.3)%, P<0.001, η2p = 0.79) is seen simultaneously. Also with an increase in resistance an increase in ME (+0 W: 4.0 (0.2)%, +10 W: 6.0 (0.3)%, +20 W: 7.0 (0.2)%, P<0.001, η2p = 0.92) and FEF (+0 W: 59.0 (2.9)%, +10 W: 66.1 (3.4)%, +20 W: 70.2 (2.4)%, P<0.001, η2p = 0.56) was found.InterpretationA cadence of 52 rpm against a higher resistance of about 35 W leads to a more optimal direction of forces and is more mechanically efficient than propelling at a higher cadence or lower resistance. Therefore, changing gears on a handcycle is important, and it is advised to keep the linear hand velocity relatively low for locomotion purposes.

A Modeling Framework to Investigate the Radial Component of the Pushrim Force in Manual Wheelchair Propulsion

The ratio of tangential to total pushrim force, the so-called Fraction Effective Force (FEF), has been used to evaluate wheelchair propulsion efficiency based on the fact that only the tangential component of the force on the pushrim contributes to actual wheelchair propulsion. Experimental studies, however, consistently show low FEF values and recent experimental as well as modelling investigations have conclusively shown that a more tangential pushrim force direction can lead to a decrease and not increase in propulsion efficiency. This study aims at quantifying the contributions of active, inertial and gravitational forces to the normal pushrim component. In order to achieve this goal, an inverse dynamics-based framework is proposed to estimate individual contributions to the pushrim forces using a model of the wheelchair-user system. The results show that the radial pushrim force component arise to a great extent due to purely mechanical effects, including inertial and gravitational forces. These results corroborate previous findings according to which radial pushrim force components are not necessarily a result of inefficient propulsion strategies or hand-rim friction requirements. This study proposes a novel framework to quantify the individual contributions of active, inertial and gravitational forces to pushrim forces during wheelchair propulsion.

A New Postural Force Production Index to Assess Propulsion Effectiveness During Handcycling

The aim of this study was to propose a new index called Postural Force Production Index (PFPI) for evaluating the force production during handcycling. For a given posture, it assesses the force generation capacity in all Cartesian directions by linking the joint configuration to the effective force applied on the handgrips. Its purpose is to give insight into the force pattern of handcycling users, and could be used as ergonomic index. The PFPI is based on the force ellipsoid, which belongs to the class of manipulability indices and represents the overall force production capabilities at the hand in all Cartesian directions from unit joint torques. The kinematics and kinetics of the arm were recorded during a 1-min exercise test on a handcycle at 70 revolutions per minute performed by one paraplegic expert in handcycling. The PFPI values were compared with the Fraction Effective Force (FEF), which is classically associated with the effectiveness of force application. The results showed a correspondence in the propulsion cycle between FEF peaks and the most favorable postures to produce a force tangential to the crank rotation (PFPI). This preliminary study opens a promising way to study patterns of force production in the framework of handcycling movement analysis.

Effects of Intramuscular Trunk Stimulation on Manual Wheelchair Propulsion Mechanics in 6 Subjects With Spinal Cord Injury

ObjectiveTo quantify the effects of stabilizing the paralyzed trunk and pelvis with electrical stimulation on manual wheelchair propulsion. DesignSingle-subject design case series with subjects acting as their own concurrent controls. SettingHospital-based clinical biomechanics laboratory. ParticipantsIndividuals (N=6; 4 men, 2 women; mean age ± SD, 46±10.8y) who were long-time users (6.1±3.9y) of implanted neuroprostheses for lower extremity function and had chronic (8.6±2.8y) midcervical- or thoracic-level injuries (C6-T10). InterventionsContinuous low-level stimulation to the hip (gluteus maximus, posterior adductor, or hamstrings) and trunk extensor (lumbar erector spinae and/or quadratus lumborum) muscles with implanted intramuscular electrodes. Main Outcome MeasuresPushrim kinetics (peak resultant force, fraction effective force), kinematics (cadence, stroke length, maximum forward lean), and peak shoulder moment at preferred speed over 10-m level surface; speed, pushrim kinetics, and subjective ratings of effort for level 100-m sprints and up a 30.5-m ramp of approximately 5% grade. ResultsThree of 5 subjects demonstrated reduced peak resultant pushrim forces (P≤.014) and improved efficiency (P≤.048) with stimulation during self-paced level propulsion. Peak sagittal shoulder moment remained unchanged in 3 subjects and increased in 2 others (P<.001). Maximal forward trunk lean also increased by 19% to 26% (P<.001) with stimulation in these 3 subjects. Stroke lengths were unchanged by stimulation in all subjects, and 2 showed extremely small (5%) but statistically significant increases in cadence (P≤.021). Performance measures for sprints and inclines were generally unchanged with stimulation; however, subjects consistently rated propulsion with stimulation to be easier for both surfaces. ConclusionsStabilizing the pelvis and trunk with low levels of continuous electrical stimulation to the lumbar trunk and hip extensors can positively impact the mechanics of manual wheelchair propulsion and reduce both perceived and physical measures of effort.

Hand-rim Forces and Gross Mechanical Efficiency at Various Frequencies of Wheelchair Propulsion

To determine the effects of push frequency changes on force application, fraction of effective force (FEF) and gross efficiency (GE) during hand-rim propulsion. 8 male able-bodied participants performed five 4-min sub-maximal exercise bouts at 1.8 ms(-1); the freely chosen frequency (FCF), followed by 4 counter-balanced trials at 60, 80, 120 and 140% FCF. Kinetic data was obtained using a SMART(Wheel), measuring forces and moments. The GE was determined as the ratio of external work done and the total energy expended. Increased push frequency led to reductions in peak resultant force (P<0.05), ranging from 167 to 117 N and peak tangential force (P<0.05), ranging from 117 to 77 N. However, FEF only demonstrated a significant difference between 60% and 140% FCF (69 ± 9% and 63 ± 7, respectively; P<0.05). Work per cycle decreased significantly (P<0.05) and rate of force development increased significantly (P<0.05) with increased push frequency. GE values were significantly lower at 60%, 120% and 140% FCF than 80% and 100% FCF (P<0.05). No meaningful associations were present between FEF and GE. Under the current testing conditions, changes in push frequency are accompanied with changes in the absolute force values, albeit without changes in either the gross pattern/trend of force application or FEF. Changes in GE are not explained by different levels of force effectiveness.

Are the force characteristics of synchronous handcycling affected by speed and the method to impose power?

Objective To investigate the influence of exercise conditions (speed and method to impose power) on the applied force, force effectiveness and distribution of work during handcycling. Method Ten able-bodied men performed handcycling on a treadmill. To test the effect of speed, subjects propelled at different velocities (1.38 m/s, 1.66 m/s, 1.94 m/s) with a constant power output (35 W). To test the effect of method to impose power, subjects cycled at a constant speed (1.66 m/s) and different power outputs imposed by incline (1%, 2.5%, 4%) versus pulley system (simulated resistance of incline conditions). From the applied forces, fraction of effective force and work production over the propulsion cycle were calculated. Results While total force (24.2 to 18.2 N) and tangential force (20.0 to 13.5 N) decreased significantly with higher speed, no change in lateral force was observed (3.5 to 2.8 N). This resulted in a significant decrease of effectiveness (82.6 to 72.9%) and in a change of relative work distribution over the propulsion cycle (44 to 29.8 J). While cycling with the highest velocity, compared to the lower velocities, more work was achieved during pulling and pressing and less work was produced while lifting the crank. No significant differences between the two methods to impose power were found in any parameter ( p < 0.05). Conclusions When propelling at equal power output, speed influences the force characteristics of handcycling and should be considered when analyzing force application. Since there is no difference in the force characteristics between propelling at an incline versus ground-level, results of studies examining handbike propulsion with either of these methods are largely comparable.

Effects of type and mode of propulsion on hand-cycling biomechanics in nondisabled subjects

This study investigated the range of motion (ROM) (in degrees) of the upper limb and trunk, forces (Newtons), two-dimensional fraction effective force (FEF(2D)) (in percent), and torque (Newton meters) during hand cycling. Seven nondisabled participants performed a 1 min exercise test at 70 rpm on a hand cycle (HC) fixed to an ergometer in synchronous (SC) mode versus asynchronous (AC) mode and in arm-power (AP) versus arm-trunk-power (ATP) type of propulsion. Higher (p < 0.001) flexion/extension of the trunk was found during ATP versus AP type and higher (p < 0.001) lateral flexion and rotation of the trunk in AC versus SC mode. The trunk ROM should explain the different force generation patterns observed in this investigation between AC and SC modes and AP and ATP types. However, kinetic results do not allow the most effective type or mode of propulsion (FEF(2D): from 72.9% to 89.3%) to be established. We conclude that trunk movement is an important parameter to consider in ergonomically optimizing hand cycling. Nevertheless, future studies in experienced HC users, especially with limited trunk function, should be performed.

The influence of altering push force effectiveness on upper extremity demand during wheelchair propulsion

Manual wheelchair propulsion has been linked to a high incidence of overuse injury and pain in the upper extremity, which may be caused by the high load requirements and low mechanical efficiency of the task. Previous studies have suggested that poor mechanical efficiency may be due to a low effective handrim force (i.e. applied force that is not directed tangential to the handrim). As a result, studies attempting to reduce upper extremity demand have used various measures of force effectiveness (e.g., fraction effective force, FEF) as a guide for modifying propulsion technique, developing rehabilitation programs and configuring wheelchairs. However, the relationship between FEF and upper extremity demand is not well understood. The purpose of this study was to use forward dynamics simulations of wheelchair propulsion to determine the influence of FEF on upper extremity demand by quantifying individual muscle stress, work and handrim force contributions at different values of FEF. Simulations maximizing and minimizing FEF resulted in higher average muscle stresses (23% and 112%) and total muscle work (28% and 71%) compared to a nominal FEF simulation. The maximal FEF simulation also shifted muscle use from muscles crossing the elbow to those at the shoulder (e.g., rotator cuff muscles), placing greater demand on shoulder muscles during propulsion. The optimal FEF value appears to represent a balance between increasing push force effectiveness to increase mechanical efficiency and minimize upper extremity demand. Thus, care should be taken in using force effectiveness as a metric to reduce upper extremity demand.

Biophysical Aspects of Submaximal Hand Cycling

Hand cycling is a popular form of wheeled mobility. This study evaluates biophysical differences between synchronous/asynchronous hand cycling. During submaximal hand cycling on a motor driven treadmill, 9 able-bodied subjects performed 2 series of 4 steady state exercise bouts at 1.11 to 2.78 m/s. Metabolic parameters, mean force on the handle bar, muscle activity and local perceived exertion in the upper body were determined. Mean power output was 35.4 +/- 7 W (v = 2.78 m/s). At this speed oxygen uptake was 1.11 +/- 0.25 and 1.26 +/- 0.26 l/min for the synchronous and asynchronous modes, respectively. Mechanical efficiency was significantly higher (v = 2.78 m/s: + 11.5 %) in synchronous cycling. Higher activity of m. obliquus externus and extensor carpi ulnaris was seen. Mean 2D total force and fraction effective force on the handle bar were lower in asynchronous hand cycling. Local perceived discomfort was higher in the asynchronous mode for different arm regions. Synchronous hand cycling is more efficient and at a lower metabolic cost. Mean muscle activation and the local perceived discomfort may explain some results. Future study should focus on combined time-based force and muscle activity characteristics. Synchronous hand cycling should be preferred during submaximal exercise in early rehabilitation.

The Effect of Visual Biofeedback on the Propulsion Effectiveness of Experienced Wheelchair Users

Kotajarvi BR, Basford JR, An K-N, Morrow DA, Kaufman KR. The effect of visual biofeedback on the propulsion effectiveness of experienced wheelchair users. Objective To determine the effect of visual feedback on the propulsion effectiveness of experienced manual wheelchair users. Design Controlled trial. Setting A motion analysis laboratory. Participants A convenience sample of 16 healthy men and 2 healthy women with T4-L2 traumatic paraplegia, a mean age of 38±9 years, and a mean duration of manual wheelchair-based mobility of 14±8 years. Intervention Propulsion was assessed as the subjects propelled an instrumented wheelchair (with and without visual biofeedback) on a custom-built dynamometer at propulsion intensities of .15 and .25W/kg for 10 minutes. Main Outcome Measures The primary outcome variable was the fraction of effective force (FEF) (ie, the ratio of effective to total force) applied by the subject to the wheelchair’s pushrim. Secondary variables included velocity, stroke frequency, and stroke angle. Results A 2-factor analysis of variance with repeated measurements was used to detect significant differences between the outcome variables. The FEF ratio was 73.9% without feedback and 72.5% with feedback at the lower-intensity level. Propulsion during the higher intensity condition both with and without feedback resulted in a statistically significant improvement in the FEF (73.9%–78.7% with no feedback, 72.5%–80.2% with feedback), compared with the lower-intensity level. Stroke angle increased from 84.3° to 98.7° and frequency decreased from 66 to 57.8 strokes/min with feedback. Conclusions Visual biofeedback may have little utility in improving the force effectiveness of manual wheelchair propulsion in experienced wheelchair users. Experienced wheelchair users may have already optimized their stroke in a manner that balances energy expenditure with stroke efficiency. Other variables such as stroke length and frequency may be more amenable to visual biofeedback.

Effect Of Seat Height During Manual Wheelchair Propulsion In Persons With A Spinal Cord Injury

Seat height in manual wheelchair propulsion appears to affect submaximal physical strain and technique. In terms of efficiency an optimum seat height was described in relation to elbow angle. PURPOSE To evaluate the effect of seat height on gross mechanical efficiency (ME), metabolic strain and propulsion technique during hand rim wheelchair propulsion in subjects with a spinal cord injury (SCI) in rehabilitation. METHODS Twelve persons with SCI (8 men, 19–77yr; C5/C6-L2; 8 incomplete) conducted 8 submaximal hand rim wheelchair exercise tests at 8 seat heights (70 to 140°; full elbow extension = 180°; relative to elbow angle in a fixed sitting posture with the hands at top-dead-center of the rim). Subjects performed the tests (4min) in a counter-balanced order on a stationary computer-control led wheelchair ergometer at an individualized power output (5.4 – 13.9W; v=0.42–0.83m/s). Last minute physiological and technique data (fraction effective force [FEF], total force [Ftot], mediolateral [Fy] and vertical force [Fz] components and push time [PT]) were evaluated using a repeated measures ANOVA (P <0.05). RESULTS All physiological data – including ME – showed significant differences (P <0.05) with seat height. Visual inspection showed a tendency for ME to optimize at 100–130° with clear detrimental values at 80 and 90°. FEF decreased (71–58%) and Ftot, Fy and Fz increased significantly with increasing seat height. PT remained constant. DISCUSSION: Physiological data indicate a tendency to optimize with seat height. This trend does not seem to relate to trends in technique data, which seem to be regulated by different task or geometry-related boundary conditions. A preliminary regression analysis showed an impact of lesion level on the physiological data. Future studies must verify the impact of lesion level on seat height results. CONCLUSIONS Optimum seat height in terms of ME in SCI during rehabilitation tends towards 100–130° elbow angle. Individual seat height evaluation seems indicated during SCI rehabilitation.

Biomechanics and Strength of Manual Wheelchair Users

Background/Objective: Previous investigations have identified muscular imbalance in the shoulder as a source of pain and injury in manual wheelchair users. Our aim was to determine whether a correlation exists between strength and push rim biomechanical variables including: tangential (motive) force (Ft), radial force (Fr), axial force (Fz), total (resultant) force (FR), fraction of effective force (FEF), and cadence.Methods: Peak isokinetic shoulder strength (flexion [FLX], extension [EXT], abduction [ABD], adduction [ADD], internal rotation [IR], and external rotation [ER]) was tested in 22 manual wheelchair users with a BioDex system for 5 repetitions at 60°/S. Subjects then propelled their own manual wheelchair at 2 speeds, 0.9 m/s (2 mph) and 1.8 m/s (4 mph), for 20 seconds, during which kinematic (OPTOTRAK) and kinetic (SMARTWHEEL) data were collected. Peak isokinetic forces in the cardinal planes were correlated with push rim biomechanical variables.Results: All peak torque strength variables correlated significantly (P = 0.05) with Ft, Fr, and FR, but were not significantly correlated with Fz, FEF, or cadence. Finally, there were no relationships found between muscle strength ratios (for example, FLX/EXT) and Ft, Fr, FR, Fz, or FEF.Conclusion: There was a correlation between strength and force imparted to the pushrim among wheelchair users; however, there was no correlation found in wheelchair propulsion or muscle imbalance. Clinicians should be aware of this, and approach strength training and training in wheelchair propulsion techniques separately.

The effect of seat position on wheelchair propulsion biomechanics

This study examined the effect of seat position on handrim biomechanics. Thirteen experienced users propelled a wheelchair over a smooth level floor at a self-selected speed. Kinetic and temporal-distance data were collected with the use of an instrumented rim and a motion analysis system. A custom-designed axle was used to change the seat position. We used repeated measures analysis of variance to evaluate if differences existed in the temporal-distance and kinetic data with change in seat position. Results showed that a shorter distance between the axle and shoulder (low seat height) improved the push time and push angle temporal variables (p < 0.0001). Tangential force output did not change with seat position. Axial and radial forces were highest in the lowest seat position (p < 0.001). Propulsion efficiency as measured by the fraction of effective force did not significantly change with seat position.